Telephone system



May 5, 1936. R. L. STOKELY TELEPHONE SYSTEM Filed Nov. 25, 1932 2 Sheets-Sheet 2 /Nl/ENTOR L. TO/(E L y B) ATTORNEY Patented May 5, 1936 UNITED STATES PATENT OFFICE Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application November 25, 1932, Serial No. 644,252

3 Claims.

This invention relates to telephone systems and particularly to improvements in private branch exchange systems.

The object of this invention is to simplify the arrangement at a private branch exchange for preventing unauthorized connections to distant exchanges from being made by private branch exchange subscribers.

In a copending application by F. A. Bonomi, Serial No. 644,235, filed Nov. 25, 1932, a system has been disclosed for preventing subscribers in private branch exchange systems from establishing connections to distant ofiices such as toll oflices if such calls are attempted over trunks leading to local offices. If such a connection is dialed, the call is answered at the toll office to which it is extended. Current of a certain polarity is thereby sent back over the local offi'ce trunk incoming to the private branch exchange. This current causes the operation of means to release the toll connection and to transfer the calling subscribers line from the local office trunk to a branch line terminating at a private branch exchange operators position.

Systems have also been provided whereby a line extended to a trunk over one switch may be transferred to another trunk over another switch, if the number dialed over the first trunk connection is of a certain combination. To this end a special stepping switch was associated with the line and actuated by the special combination to cause circuit changes to take place to switch the line from one trunk connection to another. If succeeding digits of this call indicate that still another trunk connection is desired, this second extension Will be disconnected and a third trunk or a fourth trunk connection established as desired by means of this auxiliary switch.

A. feature of this invention relates to means for preventing subscribers in private branch exchange systems from establishing connections to distant offices, such as toll offices, when such calls are attempted over trunks leading to local offices. This means comprises an auxiliary switch and. circuit arrangements therefor at the private branch exchange which, when a certain code is dialed, namely, a number of a toll office to which a call is prohibited, operate to cause the sub scribers line to be disconnected from the local ofiice trunk over which the toll call was attempted and to be connected to a special line terminating' at a private branch exchange operators position. If the subscriber dials a local office number, the auxiliary switch does not effect a transfer.

Another feature of this invention is a system of this kind in which each local office trunk is provided with an individual auxiliary switch and associated circuit arrangement.

The invention has been illustrated in the accompanying drawings in which:

Fig. 1 shows it applied to one type of automatic telephone system; and

Fig. 2 shows it applied to another type of automatic telephone system.

Referring now the the drawings, Fig. 1 shows a subscribers station I in a private branch exchange connected through switches shown in diagrammatic form at 2 to a trunk circuit 3 embodying the features of this invention. This trunk circuit may extend to a central office. Ifthe subscriber at 1 attempts to extend a connection through this central ofiice, to a toll ofiice, he dials a toll number. The first numeral dialed,

after the trunk 3 has been seized automatically,

will represent such a toll call at the central office. The arrangement may be such that the toll nun' iher to be dialed is zero or ten impulses, and also so that the preliminary digit 1 will be lost, that is, if the subscriber dials 1- no permanent effect is produced at the central ofiic'e. A local switch 4 is associated with trunk 3 having twobanks 5 and 6, an operating or stepping magnet I, a release magnet 8 and off-normal contacts 9. If

the numeral 1 should be dialed this switch will be actuated one step but will return to normal. This impulse will release relay Ill momentarily as it should be understood that relay l0 becomes operated on the seizure of the trunk 3. 0n the original operation of relay ID the slow-to-release relay II will operate and remain operated during the sending of the dial pulses in each series. On the first release of relay Ill, if it is supposed that one impulse only is sent, the magnet 1 will receive one impulse and advance the brushes of switch 4 one step. The circuit for this magnet extends from battery, winding of the magnet, lower armature and back contact of relay I Z, lower inner armature and front contact of relay II, lower armature and back contact of relay ill to ground. On the original operation of relay In acircuit was closed from battery and ground at the central office over the tip and ring conductors, armatures and back contacts of relay l5, upper armature and front contact of relay lll', winding of relay I6 and make-before-break contacts of relay M, to cause relay I 6 to operate. However, as relay l4 operates on the first impulse: on the release of relay ID the circuit for relay I6 is opened by the armature and front I ture and front contact of relay ll.

contact of this relay and releases. However, when relay l0 again operates relay [4 is released if no further impulses are received. Relay, I4 is slow in releasing so in case more than. one impulse is sent relay l4 will be maintained operated during pulsing to prevent relay [6 from operating during the dialing of a digit. This release of relay l4 at the end of a series permits the reoperation of relay I 6. Consequently, on the release of relay l4 and reoperation of relay H5, at the end of the first impulse in this case, and considering that the brushes of the banks 5 and B have advanced one step a circuit will be completed for the release magnet ..from battery through the release magnet 8, off-normal contacts 9, first terminal and brush of bank 6, lower inner armature and front contact of relay Hi to ground at the upper armature and front contact of relay l I thus causing the switch 4 to return to normal. On the next series of impulses if it is the digit that is intended for a toll call, that is, the zero'digit, the operations described are repeated, that is, relay [4 is operated and remains operated during thepulsing to maintain relay 16 released and the rotary magnet in this case advances the brushes of switch 4 to the tenth position. In this position, when the last impulse has been sent relay l4 releases and relay 16 reoperates and consequently a circuit is then completed for the operation of relay l5 from battery, the winding of this relay, the tenth terminal and brush of bank 6, lower inner armature and front contact of relay [6 to ground at the upper arma- Relay IS in operating switches the tip and ring connection from the trunk leading to the central office to leads extending to the private branch exchange operators circuit. Relay I6 is now maintained operated through the operators circuit and completes the talking connection between the calling subscriber at l and this private branch exchange operator. The talking battery for the calling subscriber is supplied through the windings of relay IB and the talking battery for the private branch exchange operator is supplied at her set in the usual manner.

' When the conversation is finished between the calling subscriber at l and the operator, relay l0 releases when the calling subscriber hangs up his receiver'and thus causes the release of relays H and I6. Relay ll closes a. circuit for the release magnet 8 from battery, off-normal contacts 9, lower inner armature and back contact of relay I l and lower armature and back contact of relay III to ground. The switch at 2 is held operated by ground on the sleeve supplied by the terminals and brushes of bank 5 until the switch 4 is returned to normal when this ground is removed, thus permitting switches at 2 to release as is well known in the art. This is to prevent the seizure of trunk circuit 3 until the auxiliary switch 4 has actually returned to normal.

' Should the calling subscriber at l dial any other intermediate number the relay [2 will be operated as soon as the brush of bank 6 stops at any of the intermediate positions, as determined by the digit dialed, by a circuit from battery, winding of relay 12, any of the intermediate terminals and the brush of bank 6 to ground at relay H as hereinbefore traced when the pulsing ceases. Relay [2 is locked at its upper armature and front contact of relay H to prevent the rotary magnet I from, operating on subsequent series of impulses transmitted to the central ofiices by pulsing relay [0. The actual pulsing in this case is now done by the upper armature and front contact of relay H! which connects the tip and ring conductors of the trunk through the connection established at the armature and front contact of relay l4. In this case the pulsing is done on the operation of relay I0 instead of the release of relay I0. At the end of each series relay I4 is released and relay I6 is reoperated to complete the talking connection.

Referring now to the modified form of the embodiment of the invention as shown in Fig. 2,

the function of this circuit is identical with that shown in Fig. 1 with the exception of the arrangement for calling a trunk. In this case if the subscriber at l attempts a toll call he may employ two different kinds of code. It will be remembered that in the circuit of Fig. l he had to dial the zero digit when making an attempt to get the trunk connection. In this case in addition to being able to call the zero digit he may also attempt to call atrunk by dialing the code'number 211, this number being chosen merely to illustrate how different types of trunk connections may be attempted having different code numbers. Assuming that all the functions of the circuit arrangement shown in Fig. 2 are the same as in Fig. 1, as far as calling the code number 1 which releases the switch 4, the calling of the numbers 5 to 9 will out through the connection to the private branch exchange operator while the numbers 2, 3, and 4 are reserved for calling on bank 6 the code number 211 and the tenth posi-. tion for the code number zero. If the code number 211 is called the brush of bank 6 will be advanced to the second position. When this position is reached relay 20 is operated from battery, winding of this relay, second terminal and the brush of bank 6, lower inner armature and front contacts of relay l 6, to ground at the upper armature and front contact of relay ll. Relay 20 is looked through its upper armature and front contact to the same ground on relay ll, then when the next numeral is called, that is 1, a connection I is established for the operation of relay 2| from battery, winding of this relay, lower inner armature and front contact of relay 20, third terminals and brush of bank 6, to ground at relay ll. Relay 2| locks through its upper armature and front contact to ground at relay ll. When the third digit 1 of the code number 211 is called the brush of bank 6 will make a connection through the fourth terminal. In this case, therefore, a circuit will be closed for relay l5 from battery,- winding of this relay, lower armature and front contact of relay 2 l, terminal 4 and brush of bank 6 to the ground at relay II. The connection is thereby transferred from the tip and ring conductors leading to the central office to the connection leading to the private branch exchange operators position. From this point on, the operation of the two circuits is the same, relays 20 and 2| releasing on the release of relay II when the connection is released by the calling subscriber.

It should be understood that while the invention has only been illustrated in connection with two systems it could readily be applied to other embodiments without departing from the spirit thereof.

What is claimed is:

1. In a telephone system, subscribers lines, trunks, a branch line, a switch associated with each trunk, means for seizing a trunk from a calling subscribers line, dial pulse producing means; means responsive to dial pulses from said means for actuating the switch associated with said seized trunk, a relay associated with said seized trunk for disconnecting the subscribers line from said trunk and for connecting it to said branch line, another relay associated with said seized trunk for preventing further control of said switch by dial pulses, and means responsive to certain settings of said associated switch by dial pulses for operating said first relay, and means responsive to certain other settings of said switch by dial pulses for operating said second relay.

2. In a telephone system, an exchange, subscribers lines terminating in said exchange, trunks terminating in said exchange and having conductors extending outside said exchange, a branch line, means for seizing the outgoing end of a trunk from a subscribers line, a switch associated with each trunk, means operative over said calling subscribers line for setting the switch associated with said seized trunk in various positions, means responsive to the setting of said switch in certain positions for disconnecting the outgoing end of said trunk from the conductors thereof extending outside of said exchange and for connecting said outgoing end to said branch line, and means responsive to the setting of said switch in other positions for thereafter disabling said means for setting the switch.

3. In a telephone system, an exchange, subscribers lines terminating in said exchange, trunks terminating in said exchange and having conductors extending outside of the exchange, a branch line, means for seizing the outgoing end of a trunk from a subscribers line, a switch associated with each trunk, means operative over said calling subscribers line for setting the switch associated with the seized trunk in various positions, means responsive to the setting of said switch in a certain position for releasing said switch, means responsive to the setting of said switch in other positions for disconnecting the outgoing end of said trunk from the conductors thereof extending outside the exchange and for connecting said outgoing end to the branch line, and means responsive to the setting of said switch in still other positions for thereafter preventing said means for setting said switch from further control over said switch.

RAY L. STOKELY. 

